Cobalt-rare earth magnets comprising sintered products bonded with solid cobalt-rare earth bonding agents

ABSTRACT

Permanent cobalt alloy magnets of large size are prepared. At least two compacts of particulate permanent magnet cobalt alloy are provided and a layer of particles of a bonding magnetic cobalt alloy agent is deposited on the bonding surface of one compact. The bonding surface of the second compact is contacted with the deposited bonding agent substantially coextensively therewith and the resulting assembly is sintered to produce a sintered bonded composite. The bonding agent is a solid at sintering temperature.

United States Patent Martin July 1, 1975 [54] COBALT-RARE EARTH MAGNETS3,239,323 3/1966 Folweiler 65/43 COMPRISING SINTERED PRODUCTS 3,370,3422/1968 Argyle et a1. 29/472.7 3,655,463 4/1972 Benz 148/101 BONDED WITHSOLID COBALT-RARE EARTH BONDING AGENTS Donald L. Martin, Elnora, N.Y.

General Electric Company, Schenectady, NY.

Filed: Jan. 7, 1974 Appl. No.: 431,126

Inventor:

Assignee:

Field of Search 148/3157, 101, 103, 105; 29/472], 473.1, 470, DIG. 1;264/56, DIG.

References Cited UNITED STATES PATENTS 2/1966 Heimke et a1. 148/3157Primary Examiner-Walter R. Satterfield Attorney, Agent, or Firm-Jane M.Binkowski; Joseph T. Cohen; Jerome C. Squillaro [5 7 1 ABSTRACTPermanent cobalt alloy magnets of large size are prepared. At least twocompacts of particulate permanent magnet cobalt alloy are provided and alayer of particles of a bonding magnetic cobalt alloy agent is depositedon the bonding surface of one compact. The bonding surface of the secondcompact is contacted with the deposited bonding agent substantiallycoextensively therewith and the resulting assembly is sintered toproduce a sintered bonded composite. The bonding agent is a solid atsintering temperature.

2 Claims, 1 Drawing Figure COBALT-RARE EARTH MAGNETS COMPRISING SINTEREDPRODUCTS BONDED WITH SOLID COBALT-RARE EARTH BONDING AGENTS The presentinvention relates to the art of cobalt-rare earth alloy permanentmagnets and more particularly it relates to the art of bonding thesemagnets to produce magnets of desired large size or geometry withoutdeleterious effect on magnetic properties.

Permanent magnets, i.e., hard" magnetic materials, such as thecobalt-rare earth alloys, are of technological importance because theycan maintain a high, constant magnetic flux in the absence of anexciting magnetic field or electrical current to bring about such afield.

Cobalt-rare earth intermetallic compounds or alloys exist in a varietyof phases. Thus far, cobalt rare earth alloys containing a substantialamount of Co R phase (in each occurrence R designates a rare earthmetal) have exhibited the best magnetic properties. However, to producea permanent magnet with satisfactory properties, the bulk Co-R alloymust be reduced to a powder which is then usually compressed in analigning magnetic field to form an aligned pressed-powder compact.Specifically, the powder particles are magnetically aligned along theireasy axis of magnetization prior to or during compaction since thegreater their magnetic alignment, the better are the resulting magneticproperties.

The aligned pressed powder or green compact is sintered to produce asintered body of the desired density. A magnetizing field is applied tothe sintered body parallel to its easy axis of magnetization, generallyat room temperature, to produce a permanent magnet.

A disadvantage of this technique is that the sintered body or magnet islimited by the size of the pressedpowder or green compact. The greencompact, itself, is limited in size because of the high pressurerequired to press the powder into a compact with sufficient strength sothat it can be handled without excessive breakage before sintering.Experience indicates that a minimum pressure of about 100,000 psi isneeded. Thus, large magnets with an area greater than 4 to 5 squareinches are difficult to make because of the need for pressure greaterthan 200 tons.

One way of making a large magnet piece is to join smaller magnetstogether. Unfortunately, a suitable joining or bonding medium has notbeen found. Low temperature bonding with solder or epoxy cement has beenused to join cracked sintered pieces. The solder or epoxy bonding methodwhile attractive for many applications, limits the use of such bondedmagnets at elevated temperatures, particularly at temperatures in therange of 100C to 200C which deteriorate these bonding agents and weakenthe bond significantly. Also, materials such as solder or epoxy cementare nonmagnetic thereby introducing an air gap which dilutes themagnetic properties of the joined magnets some what.

The present process provides a method of bonding cobaltrare earth alloycompacts without having any significant deleterious effect on themagnetic properties of the resulting bonded sintered magnet composite.Also, the bond in the composite is substantially as stable at elevatedtemperatures as the bonded sintered magnets. Specifically, the presentbonding agent is a magnetic cobalt-rare earth alloy.

Those skilled in the art will gain a further and better understanding ofthe present invention from the detailed description set forth below,considered in conjunction with the figure accompanying and forming apart of the specification which is the cobalt-Samarium phase diagram. Itis assumed herein, that the phase diagram at 300C, which is the lowesttemperature shown in the figure, is substantially the same at roomtemperatures.

Briefly stated, the present process comprises providing at least twocompacts to be bonded together and sintered at a sintering temperatureranging from 900C to 1250C. Each compact consists essentially ofcompacted particulate permanent magnet alloy selected from the groupconsisting of Co-R, (Co-Fe)R, (Co- Cu)R, and (Co-Fe-Cu)R, where R is arare earth metal. A layer of particles of a bonding magnetic'alloy agentis deposited onthe bonding surface of one of the compacts, said agentbeing selected from the group consisting of Co-R, (Co-Fe)R, (Co-Cu)R,and (Co-Fe-Cu)R, where R is a rare earth metal. The bonding agent is asolid at sintering temperature and contains the rare earth metalcomponent in a minimum amount of at least 0.1 atom higher than thatcontained in the compacts being bonded. The bonding surface of thesecond compact is contacted with the deposited bonding agentsubstantially coextensively therewith, and the resulting assembly issintered at a sintering temperature ranging from 900C to 1250C in anatmosphere in which it is substantially inert to bond and sinter saidassembly to produce a solid composite sintered product having a densityof at least 87%.

The rare earth metals useful in forming the present bonding agents andthe permanent magnet alloy or alloys of the present compacts are the 15elements of the lanthanide series having atomic numbers 57 to 71inclusive. The element yttrium (atomic number 39) is commonly includedin this group of metals and, in this specification, is considered a rareearth metal. A plurality of rare earth metals can also be used to formthe present cobalt-rare earth alloys which, for example may be ternary,quartenary or which may contain an even greater number of rare earthmetals as desired.

Representative of the cobalt-rare earth alloys useful in the presentinvention are cobalt-cerium, cobaltpraseodymium, cobalt-neodymium,cobaltpromethium, cobalt-Samarium, cobalt-europium, cobalt-gadolinium,cobalt-terbium, cobalt-dysprosium, cobalt-holmium, cobalt-erbium,cobalt-thulium, cobalt-ytterbium, cobalt-lutecium, cobalt-yttrium,cobaltlanthanum and cobalt-mischmetal. Mischmetal is the most commonalloy of the rare earth metals which contains the metals in theapproximate ratio in which they occur in their most common naturallyoccurring ores. Examples of specific ternary alloys includecobalt-samarium-mischmetal, cobalt-ceriumpraseodymium,cobalt-yttrium-praseodymium, and cobalt-praseodymium-mischmetal.

[n the present process at least two compacts are provided which are tobe bonded together and sintered at a sintering temperature ranging from900C to 1250C. Each compact consists essentially of compactedparticulate permanent magnet alloy selected from the group consisting ofCo-R, (Co-Fe)R, (Co-Cu)R, and (Co-Fe- Cu)R, where R is a rare earthmetal or metals. The permanent magnet alloy can be formed by a number ofconventional methods and converted to particulate form in a conventionalmanner. Its particle size may vary and it can be in as finely divideda'form as desired. For most applications, average particle size willvary from about 1 micron or less to about 10 microns. Larger sizedparticles can be used but the maximum intrinsic coercive forceobtainable is lower because it decreases with increasing particle size.The powder particles are magnetically aligned along their easy orpreferred axis of magnetization prior to or during compression since thegreater the magnetic alignment, the better are the resulting magneticproperties. The aligned powder is pressed to a compact of desired sizeand shape. Compression can be carried out by a number of conventionaltechniques such as hydrostatic pressing or methods employing steel dies.The density of the aligned compacts generally ranges from about 70 to80% of theoretical.

The present bonding agent is a solid at room temperature and at elevatedtemperature ranging up to and including sintering temperature, and it isan alloy selected from the group consisting of Co-R, (Co-Fe)R, (Co-Cu)R,and (Co-Fe-Cu)R, where R is a rare earth metal or metals. The agent canvary in composition which can be determined from the phase diagram forthe particular system or which can be determined empirically. Forexample, the accompanying figure shows that for the Co-Sm system, at asintering temperature of 1100C, the solid bonding agent can obtainsamarium in a maximum amount of about 42 atom The present bonding-agentis one which is at least 0.1 atom and preferably at least 5 atom richerin rare earth metal content than that of the compacts being bonded.

' This richenrare earth metal content is necessary to at- The bondingsurfaces ofthe compacts are not even.

or level surface but have a roughness corresponding to the projectionsof the compacted particles. Although the particle size of the bondingagent can vary, it is preferably very fine in size so that when it isdeposited on the uneven bonding surface of the compact, it will contactbonding surface between projections and thereby be in contact with alarger bonding surface area resulting in a stronger bond being formedduring sintering. Specifically, since the particles in the compactgenerally range from about 1 micron to microns in size, the presentbonding agent also preferably will range from about 1 micron to 10microns in size. A bonding agent having a particle size significantlyhigher than 10 microns will not contact sufficient area of the bondingsurface during sintering to produce a suitable bond. Specifically, theparticles of bonding agent should be in contact with at least 50% of thesurface area being bonded.

In carrying out the process of the present invention, a layer of thebonding alloy agent particles is deposited on a surface of one of thealigned compacts to be bonded. Since the aligned compact is somewhatmagnetic, the deposited particles cling to its surface. The particularamount of the bonding agent deposited should be sufficient to result ina good bond in the sintered composite product and is determinableempirically. Preferably, the bonding agent is deposited to form acontinuous layer or deposit on the bonding surface. The surface of thesecond compact to be bonded is then placed in contact with the depositedlayer substantially coextensively therewith.

The resulting assembly is heated to sintering temperature in anatmosphere in which it is substantially inert. Frequently, the alignedcompacts are sufficiently magnetic so that the assembly holds together,if maintained vertically, until the Curie temperature is reached andthen just the weight of one compact on top of the other will hold ittogether during sintering. However, if desired, the assembly can besupported or held together by'conventional means such as a clamp.

The assembly is sintered in a substantially inert atmosphere to producea solid sintered composite wherein the pores are substantiallynon-interconnecting, which generally is a sintered composite having adensity of at least about 87% of theoretical. Such non-interconnectivitystabilizes the permanent magnet properties of the composite productbecause its interior is protected against exposure to the ambientatmosphere.

The present permanent magnet type cobalt alloy systems require asintering temperature ranging from 900C to 1250C. The particularsintering temperature depends largely on the particular cobalt alloysystem being sintered. For example, for Co,-,Sm type alloys a sinteringtemperature of 1 120C is particularly satisfactory. v

The sintered composite is cooled, preferably, in an atmosphere in whichit is substantially inert, preferably to room temperature. A magnetizingfield is applied to the sintered composite along its easy axis ofmagnetization, preferably at room temperature, to produce a permanentmagnet.

The density of the sintered composite may vary. The particular densitydepends largely on the particular permanent magnet properties desired.In the present invention, the density of the sintered composite rangesfrom about 87 to lO0% of theoretical.

Specifically, magnet composition and sintering techniques particularlyuseful in the present invention are disclosed in US. Pat. Nos.3,655,464; 3,655,463; and

3,695,945, all filed in the name of Mark G. Benz, and

assigned to the assignee hereof, and all of which by reference are madepart of the disclosure of the present application. Each of theaforementioned patents discloses a process for preparing novel sinteredcobaltrare earth intermetallic products which can be magnetized to formpermanent magnets having stable improved magnetc properties.

The solid composite of the present invention has a bond' or joint whichis visible to the naked eye. This bond is magnetic so that it does notdiminish the prop- 5 upon the other, coextensively with each other andsintered, to form the desired bonded sintered composite structure.

The. present invention is useful for preparing large A magnetizing fieldof 60 kiloersteds was applied at room temperature along the easy axis ofmagnetization to the control sample as well as the bonded composite andtheir magnetic properties were determined as and/or complex permanentmagnet structures for such 5 shown in the following table where: diverseapplications as meters and instruments, mag- B is the saturationinduction. netic spafatofs, p and microwave devices- B, is the residualor remanent induction, i.e., the flux The mvention ls furtherillustrated by the following h th li d ti fi ld is reduced to zero,example. i Normal coercive force H is the field strength at 10 which theinduction B becomes zero.

EXAMPLE Particles of a 66 7 wt 7 cobalt 33 3 wt 7 samarium 4 gi HR helpscharacterslze i Squareness of the g, 1r emagnetization curve. peciically, 1-1,, is the de- 23 5 7 l'j l t fig t W1th P li t Q f i fimagnetizing field required to drop the magnetization W 0 Co a W 0Samaflum a y 0 0m 3 10 percent below the remanence B That is, 41rM, Ough{mixture PQ of 63 Cobalt 37 .9 B and H is the corresponding fieldstrength. H, is samarlum' The part1cles had an average 512? Of about auseful parameter for evaluating demagnetization re- 6 microns. sistance.

A Portion of the miXture was magnetically aligned The intrinsic coerciveforce H is the field strength along the easy axis by an aligningmagnetizing field of at hi h h ti ti n (3-1-1) 01' 4 i-M i Zero, 60kllO61'StClS. After magnetic alignment, it was The maximum energyproduct (Bf-D represents pressed to form a compact which was in h h p ofthe maximum product of the magnetic field H and the a bar about one inchlong and about Vs inch in diameter induction B determined on thedemagnetization curve.

TABLE 13, B, H Hi- HV. -Hm", Sample gauss gauss oers. ocrs. ocrs.l0gauss ocrs.) Density Alignment Control Sample 9,740 8,970 8,900 23.30029,500 l9.8 94.2 .977

Sample Sintercd Piece Bonded Sintcred 9,790 9,160 9,000 21,500 28,10020.7 95.1 .984

Composite and had a ackin of about 80 ercent. This sample, As shown bthe table, the resent bonded com osite P g P y P P which was the controlsample, was sintered in an atmohas magnetic properties which aresubstantially the 5 here of ar on at a tem erature of ll20C for one sameas those of the control sam le.,This illustrates P g P P hour,furnacecooled to 875C where it was heat-a ed that the resent bondln aent has no si nlficant effect g P g g for 5 hours and then cooled toroom temperature 1n the on the magnetic properties of the bondedmagnets. Same atmosphem The control sam le and the bonded com osite wereTwo additional portions of the mixture were aligned then placed inanpair oven maintained and compacted m a substantially the same manneras about 24 hours and the coolgd to room temperature Control l to formtwo conzpzictsi each in air. Force applied manually to the bondedportion of l h F z 233 $12351?sgggiifgg atgft o the composite1nd1cdatied that hiatmgl lnbairdat this ele- 31116 In l e 6f vatedtemperature i not wea en t e on percent. The bonding surface of one ofthese compacts, l i.e., the surface across the width thereof, wasplunged i z i g g 'i l i g ga i E 4 into particles of a bonding alloyagent, and when it was 1 z i a g removed therefrom, it had asubstantially continuous agne S an omposl e on even a 6 1n the name ofDonald L. Martin and asslgned to the aslayer of bondmg agent particlesclinging thereto. h f d h b f d t f The bonding alloy agent was composedof 59 Wt.% 3 lereo 1C fi 6 j cobalt-41 wt.% samarium and had a particlesize of 1 :1 Osure O f presedn E Q ere IS about 10 microns. All of thisbonding agent was a solid C 056 t g f a t h Sm ere permanfa'n at roomtemperature as well as at elevated temperav O arge Slze' e procfesscompnses providmg at least two compacts of particulate permaturesincluding smtermg temperature, and it was about nent magnet alloy,depos1t1ng a layer of part1cles of a 4 atomic rlcher 1n samarium thanthe samarlum conbonding magnet1c cobalt alloy agent on the bondlng tentof the compacts being bonded. The bonding sursurface of one compact,contacting the bonding surface face of the second compact was contactedwith the def the S c d C m act with the d sit d be di posited bondingalloy agent substantially coextensively 0 e on 0 p e ng agentsubstantially coextensively therewith, and slntertherewith to form anassembly 1n the form of a bar mg the resultlng assembly to produce asmtered bonded about one inch long. The assembly was sintered at a ocomposite. At least 1% by volume of the bonding agent temperature of1120 C for one hour then furnaceasses throu h a li uid hase at anelevated tem eracooled to a temperature of 875C where it was heat- F e gq P P aged for five hours and then cooled to room temperature in thesame atmosphere. The bonded portion of what 15 Claimed the resultingcomPosite pp as an uneven thln l. A cobalt-rare earth alloy permanentmagnet havline. The bonded portion of the composite appeared to bestrong and did not break when force was applied manually.

ing an area greater than 4 square inches and substantially uniformpermanent magnet properties throughout, said magnet consistingessentially of a sintered product consisting essentially of at least twocompacts bonded together by a magnetic bonding agent, each said compactbeing produced by providing a permanent magnet type alloy of cobalt andrare earth metal in particulate form having an average particle size upto about 10 microns, subjecting said particulate alloy to a magneticfield to align the particles along their easy axis of magnetization, andcompressing said particulate alloy into a compact having a density of atleast 70%, said sintered product being produced by depositing a layer ofparticles ranging in size up to 10 microns of a magnetic bonding agenton the bonding surface of one of said compacts substantially coveringsaid surface with said agent, said agent being a solid at sinteringtemperature and consisting essentially of cobalt-rare earth alloycontaining the rare earth component in an amount at least 5 atom greaterthan that of the alloy of each said compact with the maximum amount ofrare earth component being 55 atom contacting the bonding surface of thesecond compact with said deposited bonding agent substantiallycoextensively therewith, and sintering and bonding the resultingassembly at a temperature ranging from 900C to 1250C in an atmosphere inwhich it is substantially inert producing a solid sintered compositeproduct having a density of at least 87%.

2. -A permanent magnet according to claim 1 where R is samarium.

1. A COBALT-RARE EARTH ALLOY PERMANENT MAGNET HAVING AN AREA GREATERTHAN 4 SQUARE INCHES AND SUBSTANTIALLY UNIFORM PERMANENT MAGNETPROPERTIES THROUGHOUT, SAID MAGNET CONSISTING ESSENTIALLY OF A SINTEREDPRODUCT CONSISTING ESSENTIALLY OF AT LAST TWO COMPACTS BONDED TOGETHERBY A MAGNETIC BONDING AGENT, EACH SAID COMPACT BEING PRODUCED BYPROVIDING A PERMANENT MAGNET TYPE ALLOY OF COBALT AND RARE EARTH METALIN PARTICULATE FORM HAVING AN AVERAGE PARTICLE SIZE UP TO ABOUT 10MICRONS, SUBJECTING SAID PARTICULATE ALLOY TO A MAGNETIC FIELD TO ALIGNTHE PARTICLES ALONG THEIR EASY AXIS OF MAGNETIZATION, AND COMPRESSINGSAID PARTICULATE ALLOY INTO A COMPACT HAVING A DENSITY OF AT LEAST 70%,SAID SINTERED PRODUCT BEING PRODUCED BY DEPOSITING A LAYER OF PARTICLESRANGING IN SIZE UP TO 10 MICRONS OF A MAGNETIC BONDING AGENT ON THEBONDING SURFACE OF ONE OF SAID COMPACTS SUBSTANTIALLY COVERING SAIDSURFACE WITH SAID AGENT, SAID AGENT BEING A SOLID AT SINTERINGTEMPERATURE AND CONSISTING ESSENTIALLY OF COBALT-RARE EARTH ALLOYCONTAINING THE RARE EARTH COMPONENT IN AN AMOUNT AT LEAST 5 ATOM %GREATER THAN THAT OF THE ALLOY OF EACH SAID COMPACT WITH THE MAXIMUMAMOUNT OF RARE EARTH COMPONENT BEING 55 ATOM %, CONTACTING THE BONDINGSURFACE OF THE SECOND COMPACT WITH SAID DEPOSITED BONDING AGENTSUBSTANTIALLY COEXTENSIVELY THEREWITH, AND SINTERING AND BONDING THERESULTING ASSEMBLY AT A TEMPERATURE RANGING FROM 900*C TO 1250*C IN ANATMOSHERE IN WHICH IT IS SUBSTANTIALLY INERT PRODUCING A SOLID SINTEREDCOMPOSITE PRODUCT HAVING A DENSITY OF AT LEAST 87%.
 2. A permanentmagnet according to claim 1 where R is samarium.